1. Field of the Invention
The present invention relates to a machining time prediction device, and more particularly, to a machining time prediction device in wire discharge machining.
2. Description of the Related Art
Since wire discharge machining requires a very long machining time, in many case, the wire discharge machining is performed in an unattended manner. Therefore, in some cases, a machining end time is unclear, and after the machining is ended, a workpiece is left along, the workpiece is rusted. In addition, since the machining time is long, a predicted machining time is information necessary for estimating work cost.
In order to solve the above-described problems, for example, JP 06-320344 A discloses a technique of obtaining a total machining path length through simulation of automatic operation and obtaining a predicted machining time through (total machining path length)÷(predicted machining speed) by using a predicted machining speed based on a machining condition indicated by screen setting or a machining program. In addition, JP 03-111125 A discloses a technique of calculating an average machining speed of machining-completed path from a machining-completed path length and an execution-completed machining time during automatic operation of actual machining and correcting a predicted machining time of a remaining machining path through (remaining machining path length)÷(average machining speed) by using a result of the calculation.
However, in the wire discharge machining, the machining speeds are greatly different according to a difference in workpiece thickness or machining shape such as a taper, an acute corner, or a minute-radius arc. For this reason, if only one predicted machining speed based on a machining condition is prepared, it is difficult to obtain predicted machining times of various machining paths at a good accuracy.
In addition, in the case of the method of obtaining the average machining speed from the machining-completed path length and the execution-completed machining time during the actual machining and correcting the predicted machining time of the remaining machining path by using the value, with respect to machining where a large number of shapes having high machining speeds exist in the first half of the machining and a large number of shape having low machining speeds exist in the second half of the machining, there occurs a large error in the corrected predicted machining time of the remaining machining path.
FIG. 12 is a screen of simulation of automatic operation performed in a wire discharge machining device and illustrates a machining program path, a selected machining condition number, a total machining path length and a remaining machining path length calculated through simulation, and a predicted machining time calculated from a predicted machining speed according to the selected machining condition. Before the actual machining is started, the remaining machining path length is set to have the same as that of the total machining path length.
FIG. 13 is a screen during the actual machining when the actual machining is started after the simulation illustrated in FIG. 12 and illustrates a machining-completed path so as to overlap a path according to the simulation. In the screen of FIG. 13, as the actual machining progresses, the remaining machining path length is decreased. The average machining speed is obtained from the machining-completed path length and the execution-completed machining time. Accordingly, the predicted machining time of the remaining machining path length is corrected. However, in the machining path illustrated in FIG. 13, since minute-radius arcs or acute-angle corner portions causing a decrease in machining speed are concentrated on the remaining machining path, it is considered that a larger error occurs in the predicted machining time of the remaining machining path length.
As described above, in the method of calculating the predicted machining time in the related art, since the accuracy is low, there is a problem in that it is difficult to apply the method to manage machining plan or estimate work cost.